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Washington (CNN)The Republican Party is waking up -- but it might already be too late.

Donald Trump's stroll toward the GOP presidential nomination is starting to turn the denial evident for months among key party power brokers to desperation. The mood of some in the party was aptly summed up Thursday by Republican lobbyist and former congressman Vin Weber on CNN's "The Lead" with Jake Tapper.

"All of a sudden, everybody is saying 'Oh My God — the house is burning down we should have done something before it got this far,'" said Weber, who is supporting John Kasich in the presidential race and is calling on the party to unite behind the Ohio Governor.

Sen. Marco Rubio, who pulled out of the presidential race on Tuesday after failing to take down Trump, had a grim assessment of the Republican Party's state of play on his first day back at work in the Senate on Thursday.

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"Hopefully there's time to still prevent a Trump nomination, which I think would fracture the party and be damaging to the conservative movement," Rubio told reporters.

Anti-Trump forces are getting a sense of the backlash they'd face if they deny him the nomination. Trump warned earlier this week on CNN's "New Day" that the convention could deteriorate into a "riot" if he is blocked from power.

And on Friday, a top Trump aide threatened to give up his credentials as a convention delegate and leave the Republican Party in a stark warning to the GOP about the "consequences" if Trump is blocked from the nomination.

"I will tell you this, if the Republican Party comes into that convention and jimmies with the rules and takes away the will of the people, the will of the Republicans and the Democrats and Independents who voted for Mr. Trump, I will take off my credentials, I will leave the floor of that convention, and I will leave the Republican Party forever," Sam Clovis, a national co-chair for Trump's campaign, said Friday on "New Day."

Deepening anxiety

The deepening anxiety in the GOP was underscored by a meeting in Washington Thursday of prominent conservative leaders dedicated to finding a way to prevent Trump from securing the 1,237 delegates needed for the nomination.

Trump's failure to win Ohio on an otherwise successful night of primaries Tuesday opened a narrow window for opposing forces in the Republican Party to wrest the nomination from him because it lengthened his odds of winning a majority of delegates. If he does fall short, Trump could face an acrimonious contested convention in Cleveland in July.

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Conservative activist Erick Erickson raised the specter of a "unity" ticket to stop Trump in a statement he issued after the meeting, noting that the party's revered icon Abraham Lincoln was not nominated until after the third convention ballot.

"We believe that the issue of Donald Trump is greater than an issue of party," the statement read. "It is an issue of morals and character that all Americans, not just those of us in the conservative movement, must confront."

One person at the meeting, Deborah DeMoss Fonseca, a former aide to late Sen. Jesse Helms, said that there was "definitely a consensus of not wanting Donald Trump."

"I think there's still several scenarios that could play out. And I think this particular group will look for whatever it is that's going to do it," she said.

Concerted effort

Thursday's meeting was especially intriguing because it appeared to be the most concerted effort yet by the conservative movement, many of whose adherents view the New York real estate mogul as a political apostate, to stop Trump.

But it remained unclear whether the initiative would be any more successful than previous attempts by the Republican establishment to thwart Trump.

After all, a scorching speech by former GOP nominee Mitt Romney did nothing to slow the outspoken businessman. Nor did an extraordinary indictment by National Review, which devoted most of an issue to debunking Trump's conservative bona fides. And Trump boasted at his victory party on Tuesday night in Florida that he had won the Sunshine State despite a multi-million dollar negative ad blitz attacking him.

And every candidate who tried to destroy Trump by hammering him on policy, his past business deals or his sometimes vulgar outbursts — including Rubio, Jeb Bush, Rick Perry and Bobby Jindal -- only succeeded in sinking their own presidential prospects.

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The conservative uprising on Thursday was not the only eye-opening example of the Stop Trump movement.

Former GOP candidate Lindsey Graham, who once said choosing between Trump and Cruz would be like picking between being shot and poisoned, made his choice. The South Carolina Senator told CNN's Dana Bash that he was now lining up behind the Texas Senator and would help raise money for him.

Graham admitted that Cruz was "not well liked" among his peers on Capitol Hill, but implied he was the lesser of two evils.

"I have doubts about Mr. Trump," Graham said. "I don't think he's a Republican, I don't think he's a conservative, I think his campaign's built on xenophobia, race-baiting and religious bigotry. I think he'd be a disaster for our party and as Senator Cruz would not be my first choice, I think he is a Republican conservative who I could support."

Fundamental weakness

The most fundamental weakness in any organized effort to stop Trump in the remaining contests in the Republican nomination is the math after more than half the states have voted.

The billionaire only needs to win 55.5% of the remaining delegates to be awarded, according to a CNN estimate.

Although he has only won 47% of the delegates awarded so far, the field, now consisting of just Trump, Cruz and Kasich, is much narrower than before and some contests are now winner take all affairs and do not hand out delegates proportionally as was the case in many previous contests.

Republican political strategist Phillip Stutts said the next six weeks will be crucial in defining whether any attempt to deprive Trump of the nomination would even be possible.

"If Trump is not slowed down, there is not a convention fight to be had," Stutts said, pointing to a set of northeastern primaries on April 26 in Connecticut, Delaware, Maryland, Pennsylvania and Rhode Island as critical to foes bent on stopping Trump.

Another complication for the anti-Trump forces is that the billionaire could be the strongest force in a string of coming primaries. To slow his march, Kasich must show he can harvest more than the single victory he has so far -- on his home ground of Ohio.

Alternatively, Cruz, who is Trump's closest rival with 418 delegates to the billionaire's 678, according to a CNN estimate, would have to show an appeal outside conservative heartland states that he is yet to demonstrate on a large scale.

The strength of Trump's position has some of his allies warning that any attempt to snatch victory from his grasp would not just be unfair, it would be futile.

"Donald Trump is the will of the people. We need to listen to the people, back his candidacy and win in November," said Florida Gov. Rick Scott on CNN's "The Lead" with Jake Tapper on Thursday.

Hopes that a compromise candidate could emerge at a contested convention also took a blow on Thursday when House Speaker Paul Ryan ruled himself out — though he admitted that a delegate showdown was becoming more likely in Cleveland.

As the idea of the first contested convention in decades is gathering steam, the institutional leadership of the Republican Party finds itself in an unenviable position.

Any attempt to deprive Trump of the nomination would not just cause uproar in a year in which establishment politicians have been toppled. It would effectively mean the disenfranchisement of 7.5 million voters who have backed Trump in the primary process so far -- voters who the GOP can ill afford to lose at a time when national demographics give Democrats an easier route to the White House.

That's why officials like Republican National Committee Communications Director Sean Spicer say that the process of selecting a nominee must be inviolate if a candidate reaches the magic number of 1,237 delegates.

"Our job is to wait until the voters decide who that nominee will be," Spicer told Wolf Blitzer on CNN's "The Situation Room," calling on Republicans to unite to fight for the "bigger prize" -- depriving the Democrats of the White House.

If the latest attempts to thwart Trump fail, and party power brokers decide they cannot stomach the Republican nominee, there may be a third option by embracing the final stage of grief — acceptance — and trying to limit the damage that they believe having Trump at the top of their ticket would unleash.

That could mean striving to ensure that even if Democrats win the White House, they are unable to boost an incoming president by making significant gains in Congress.

"Keeping the majorities in the Senate and the House is for us where the donors should be putting their money," said Stutts.